They are owls. Image: Warner Bros.
The decision was apparently made after exactly one performance, when Tuesday's first preview show included a moment where an owl escaped into the theatre, rather than returning to its handler. Oops.
Funny tech mishap: a live owl went to its spot then flew away. They couldn’t get it back and I’m not sure they have yet. Crew was scrambling
— Andrew Sims (@sims) June 7, 2016
So the producers decided to nix the owls, changes, they explained, being part of the usual previews process. "The production of Harry Potter and the Cursed Child is currently in its preview stage, with the process designed to allow the creative team time to rehearse changes or explore specific scenes further before the play's official opening," said the producers' statement. "As part of this process earlier this week the decision was made not to feature live owls in any aspect of the production moving forward."
As a result, when audiences got to the theatre on Thursday for part two of the play, they were greeted by a sign that read:
During the performance you may see some birds in cages but please note that these birds aren't real — just very realistic pieces from our brilliant props department!
There are no real birds featured in the production.
It should have added "...anymore" there at the end.